In a letter to Keith Vaz MP, Metropolitan Police Commissioner Sir Bernard Hogan-Howe revealed Othona, which started in May 1994 and lasted three years, had a budget of nearly £8 million.

Sir Bernard, who came under considerable pressure in front of the Home Affairs Select Committee earlier this week over the destruction of the files, also revealed the cost of the Met's phone hacking investigation, Operation Weeting, has hit £16.9 million.

Mr Vaz said "I t is deeply worrying that vital evidence may have been shredded from Operation Othona, an investigation which lasted a number of years and was budgeted to cost the taxpayer over £7.8 million."

Sir Bernard admitted earlier this week he had not contacted his predecessors over claims the Othona files had been shredded and said he had not asked to see a 2012 memo that reportedly summarises their contents

Written by detective s uperintendent David Hurley and uncovered by Mr Ellison, the memo reveals officers stole and trafficked illegal drugs, shared reward payouts with informants, sold confidential police intelligence to criminals and fabricated applications for more rewards and accepted bribes to destroy and fabricate evidence.

Mr Vaz requested a breakdown of the costs of 10 separate Met investigations, for which details of nine were provided.

Operation Elveden, an investigation into corrupt payments to public officials from journalists, has cost £9.2 million so far, while Kalmyk, the operational name of an investigative strand of inquiry relating to computer hacking offences, has cost £2.5 million.

Herne, into the activities of undercover police, has cost £3.15 million.

Yewtree, into allegations of sexual abuse by Jimmy Savile and others, has cost £3.75 million, Fairbank, into historic sexual abuse of children at Elm Guest House, in Barnes, London, has cost £720,000 and Pallial, into historic child abuse in North Wales, has cost £774,000.

Operation Alice, which investigated allegations regarding an incident between Andrew Mitchell MP and police at Downing Street, later dubbed the "plebgate affair", cost £271,460 but is expected to reach £300,000.

Mr Vaz added: " The public will be concerned to know that the estimated cost of all these investigations, which include historical operations going back a number of years, has now reached over £45 million.

"It is essential that when these investigations are conducted they are acted upon, especially when they come at a great cost to the public."

He went on: "All of these issues must have clearly put the Met under financial strain particularly considering the cuts in their budget."

Yesterday, the Met's Deputy Commissioner Craig Mackey, said a ''catastrophic'' IT failure was to blame for the loss of files on police corruption.

Mr Mackey said the Othona files were shredded after they were transferred on to an electronic database which ''corrupted and collapsed'' in 2005.

He added the force was investigating whether all the Operation Othona files were transferred to the database which ''suffered a catastrophic failure in 2005''.